Conventionally, there has been used a technique for comparing (i) input image data obtained by reading a document image with a scanner with (ii) a prestored image, for determining similarity between the input image data and the prestored image, and for, when having determined that the input image data is similar to the prestored image, prohibiting a process (such as copying) from being performed on the input image data.
Examples of a method for determining similarity include: a method for extracting a keyword from an image with use of an OCR (Optical Character Reader) or the like so as to carry out matching with the keyword; a method in which a target image is limited to an image with ruled lines and matching is carried out based on features of the ruled lines; and a method for determining similarity in accordance with distribution of color components of input image data and a reference image.
Furthermore, patent Document 1 (Japanese Unexamined Patent Application Publication No. 282088/1995 (Tokukaihei 7-282088; published on Oct. 27, 1995) discloses a technique in which a descriptor that is invariable to distortion caused by digitalization of an input document or to a difference between the input document and a matching document in a document database is generated based on features of the input document, and matching between the input document and a document in the document database is performed using the descriptor and a descriptor database which stores descriptors and which indicates a list of documents including features from which descriptors are extracted. In the technique, when the descriptor database is scanned, votes for individual documents in the document database are accumulated, and a document with the largest number of votes obtained or a document whose number of votes obtained is over a certain threshold value is considered as a matching document.
Furthermore, an example of a technique for controlling a process for input image data in accordance with the result of similarity determination is as follows: in order to prevent forgery of paper currency or stock certificate by a color image forming apparatus, it is determined whether input image data is identical with image data such as paper currency or stock certificate (reference image) or not based on a pattern extracted from the input image data, and when the input image data is identical with the image data of the reference image, a specific pattern is given to an output image so as to specify the image forming apparatus that carries out copying, a copied image is daubed, or copying is prohibited.
However, although the foregoing technique can limit (e.g., give a specific pattern, daub a copied image, or prohibit copying) the content of a process for input image data in cases where the input image data is similar to the reference image, the foregoing technique sets the content of a process for input image data in such a constant manner (as to give a specific pattern, daubs a copied image, or prohibit copying) in accordance with whether or not the input image data is similar to the reference image. This causes such problems as a low degree of freedom and unavailability.
For example, in recent years, a large number of corporations and the like often have their office provided with multi-function printers each including a copy function, a facsimile function, a filing function, an electronic delivery function, and the like. Further, these multi-function printers are often shared by a plurality of users or a plurality of groups. Moreover, in such a case, it is usual to wish to perform a process (e.g., copying, facsimile transmission, filing, or electronic distribution) on a document (input image data) in accordance with a predetermined processing rule set for each user or each group. Further, it is usual to wish to perform a predetermined process on a document in accordance with the type of the document or the like.
However, the foregoing technique only considers limiting a process for a document in cases where the document is similar to reference image, and cannot set the content of the process in accordance with a result of matching with a user, a group to which the user belongs to, the type of the document, or the like. This makes it necessary for the user to take the trouble to set the content of a process in detail every time he/she performs a process such as copying, facsimile transmission, filing, or electronic distribution on a document.
Further, the foregoing technique makes it necessary to store a reference image or features of the reference image in a memory provided in an image processing apparatus. However, because the memory capacity of the memory of the image forming apparatus is limited, the number of images that can be stored is also limited. For this reason, in particular, in cases where a plurality of users or a plurality of groups shares a single image processing apparatus, the number of images that can be stored by each user or each group is reduced.
Further, when an increase in the number of reference images causes a shortage of memory capacity, a change in memory capacity may be made by replacing a memory. However, it is in fact difficult to replace (i) a memory in which reference images have already been stored with (ii) another memory during use of a system.